Arrangement to raise the breakdown strength of insulators



W. PETERS Feb. 29, 1944.

ARRANGEMENT TO RAISE THE BREAKDOWN STRENGTH OF INSULATORS Filed Dec. l5, 1940 :NVENTQR WILHELM P ER ATTORNEY Patented Feb. 29, 1944 UNITED ARRANGEMENT TO RAISE THE BREAK- DOWN STRENGTH OF INSULATORS Wilhelm Peters, Berlin, Germany; vested in the Alien Property Custodian Application December 13, 1940, Serial No. 369,971 In Germany June 5, 1939 (KCl. 174-211) 8 Claims.

This invention relates to a novel arrangement to raise the breakdown strength of insulators which are particularly adapted for use with high frequency apparatus.

The breakdown or puncture strength of insulators is largely a function of the length of the shortest ashover path on the surface of the insulator, inasmuch as the puncture strength of the insulator is mostly far greater than the flashover strength taken along the surface thereof. Now, while a path through free air is caused to break down only in the presence of a field intensity of around kv. per centimeter, a ilashover will happen on the surface of an insulator in the presence of a field intensity being equal to about one-fifth the said value, that is to say, at around 4 to 5 kv./cm. because of capacity effects. If the surface is moreover moistened by water, as is true, for instance, in the case of rain. the said dash-over strength will be still further diminished, that is, to about one-half. Now, the purpose of the invention is entirely to obviate such decrease in the dash-over potential as caused by rain or moisture, with the result that the flashover strength of an outdoor insulator of a given size is raised to twice its ordinary value.

The present invention proves particularly appropriate and valuable where applied to the base insulators of radio transmitter towers. In the case of these, the eiiects of rain are particularly unfavorable for the reason that the mast, itself, catches a considerable quantity of rain water, and most of this runs down to the ground over the surface of the base insulators unless suitable protective means are adopted to prevent this.

It is known in the art to mount umbrella-like elements or sheds above the insulator, both with a View to protecting the base insulator from downowing water as well as from the rain hitting it from the sides, in order to thus keep its surface in dry condition. The water will thus drip down the edges of the shed without touching the insulator. However, this arrangement does not eliminate the drawback because of the inevitable pres` ence of drop formation, corona and brush-discharge phenomena are caused to arise, especially where radio frequency is concerned, and this fact tends to impair considerably the quality and efciency of radio transmission work. Where the water is copious, say, during a cloudburst in tropical regions particularly, the insulator would be bridged by an uninterrupted stream of water of a length not exceeding the length of the insulator, with the result that the insulator is shortcircuited. Where this condition prevails, the

ilashover strength would be reduced at least onehalf, if not to a still lower gure.

Now, the present invention creates conditions so that the said shortcomings are avoided by draining the water to ground through a separate drain duct without permitting drop formation so that the eld intensity of the thread or tube oi water assumes such a low figure that practically no current is conducted any more.

This invention will best be understood by referring to the accompanying drawing in which:

Fig. 1 is a vertical section of one embodiment of the invention; and, Fig. 2 is an. elevation partly in section of another embodiment of the invention.

As shown in Fig. 1, the drain conduct l by virtue of the fact that it is spiraled, has a length being a multiple of the length of the base insulator 2 so that in the drain tube no 'flashover is likely to occur any more. To collect the waiter running down the mast, a basin is provided above the insulator, as indicated at 3. The said basin extends beyond the connes of the insulator to an extent or point so that the surface thereof is protected from lateral rain. The water nally is drained through the drain pipe 4 which ccnnects with the ground or soil. By using a spiraled drain duct, especially where radio frequency is dealt with, electrical currents are precluded completely owing to the circumstance that the inductance of this drain spiral conjointly with the base capacitance of the mast alone or additionally with a distinct capacity, is tuned roughly to resonance so that even where the water possesses high conductivity no electrical currents are able to flow to ground because of the stopper eifect of the parallel resonance circuit. The tuning of the said assembly could be altered whenever there is a change in the operating wavelength. In this case, the drain duct which should normally be made of insulation material, such as ceramic, could wholly or partly =be built of metal.

To prevent the draining water from dripping upon the lower electrodes, according to a further object of the invention as shown in Fig. 2, the water at the end of the insulator is led away right through a duct or bore inside the insulator. This makes for a still further improvement in the breakdown or llashover strength of the insulator. In fact, the thread of water has now no longer any connection between the live electrodes. Separation or isolation of the thread of water could also be insured according to the invention by combining disc-shaped or spiral sheds,

that is to say, by mounting them alternately in a certain way along the insulator.

What is claimed is:

l. A high frequency insulator having means for increasing the voltage flash-over strength when subjected to moisture and high voltages comprising a body of insulating material, a moisture collecting basin secured to said body, a spiral-shaped fluid duct extending from the lower inside portion of said basin and extending down through the inside of said body to a point' below its base to drain the moisture collected by said basin. y k v 2. A high frequency insulator having means for increasing the voltage :dash-over Vstreng-,ith when subjected to moisture and high voltages comprising a body of insulating material vhaving' a helical outside contour, a moisture lcollecting basin securedto said body at the lower end of y said helical outside contour portion, a fluid duct extending from the lower inside portion of said basin and extending down through the inside of said body to a point below its base to drain the moisture collected by said basin.

3. A high frequency insulator for a radio transmitter having means for increasing the voltage iiash-over strength when subjected to moisture and high voltages comprising a body of insulating material, a 'moisture collecting basin secured to said body, a fluid duct extending from the lower inside portion of said basin and extending down through the inside of said body to a point below its base to drain the moisture collected by said basin, said fiuid duct being tuned to the resonant frequency at which said transmitter is to operate.

4. A high frequency insulator for a radio transmitter having means for increasing the voltage flash-over strength when subjected to moisture and high voltages comprising a hollovtT cone-shaped body of insulating material, a moisture collecting basin secured to said body, a spiral-shaped uid duct extending from the lower inside portion of said basin and extending down through the inside of said body to a point below its base to drain the moisture collected by said basin, said uid duct being tuned to the resonant frequency at which said transmitter is to operate.

5. Apparatus as described in claim 3 wherein said body is in the form of an annular member with plate means at the top and bottom thereof and with said iiuid duct positioned within said annular member with its inlet opening connected to said basin through the top plate means and with its outlet opening connected through the bottom `plate means.

6. A high frequency insulator having means for increasing' the voltage hash-over strength when subjected to moisture and high voltage comprising, a body of insulating material positioned between a zone of high potential and a zone of low potential, fluid-directing means to direct fluid which is received by said insulator in said zone of high potential, and means form- 'ing a fluid duct extending from said fluid-directing means to said Zone of low potential to drain moisture from said Zone of high potential, said uid duct being tuned to be resonant at substantially the operating frequency.

'7.'A high frequency insulator having means for increasing the voltage flash-over strength when subjected to moisture and high voltage comprising, a body of insulating material positioned between a zone of high potential and a zone of low potential, and water directing means extending from said zone of high potential to said zone of low potentialand directing the water along a substantially arcuate path the electrical inductance of which path is of a value at the operating frequencies that it forms with the capacitance present a wave trap which prevents any substantial flow of electrical current along said path.

8. A high frequency insulator for withstanding high voltage of predetermined operating frequencies comprising, a body of insulating material, shield means at the top of said body for diverting moisture from said body, and uid-directing means forming a solenoidal passageway substantially from the top to the bottom of said body to carry the moisture from said shield means along a solenoidal path from the top of said body to the bottom thereof with the inductance of the path being such that it forms with the capacitance of the insulator a wave trap l which is effective to block the ow of current of the operating frequencies, whereby a by-pass is provided for the moisture whereas electrical current of the operating frequencies will not now along said path.

WILHELM PETERS. 

